1. Field of the Invention
The present invention relates to a method of observation by the transmission electron microscopy, and particularly to an observation method by the transmission electron microscopy capable of clearly observing the distribution condition of defects such as pores in an amorphous material.
1. Discussion of the Background
Through the process of development of various materials and of devices, grasping the distribution condition of defects in an amorphous material is a critical issue. In the development of semiconductor integrated circuit devices, for example, the interconnection rule has entered a generation of 100 nanometer level, thus the higher integration requires a multilayer interconnection structure applying an interconnection layer made of copper and an interlayer insulating layer made of an insulating material.
In a semiconductor device having that type of multilayer interconnection structure, the dielectric constant of the insulating material structuring the interlayer insulating film is required to be decreased to reduce the parasitic capacitance between interconnections. An effective method to reduce the dielectric constant of insulating materials such as SiOx is to form a porous (low-k) material by introducing pores therein.
However, in the case that the semiconductor integrated circuit is formed using a porous insulating material, the three-dimensional shape and the distribution of pores give significant influence on the mechanical and electrical characteristics of the interlayer insulating film. For instance, when pores penetrate the insulating film to create continued pores, they form what is called the “leak path” , which induces leak current and degradation in withstand voltage of the device element.
Accordingly, it is very critical to grasp the three-dimensional shape and the distribution of pores in the development of a Cu/low-k multilayer interconnection structure. There are reports on the method for evaluating the pore size, (for example, W. L. Wu et al., J. Appl. Phys., 87 p1193 (2000))
The method disclosed by W. L. Wu et al. (J. Appl. Phys., 87 p1193 (2000)), however, gives only a speculation of the three-dimensional shape and the distribution of pores through calculations based on various assumptions, and leaves unknown conditions of actual shape and distribution of pores.
In addition, for the case of multilayer interconnection structure of a semiconductor integrated circuit, for example, the interlayer insulating film is made of an amorphous material, while the metallic sections such as the interconnection layer and the copper structuring the buried plug are in a polycrystalline state. Accordingly, observation of defects or the like in the metallic sections often becomes inadequate under the same observation condition with that for the amorphous insulating layer.
To this point, the inventors of the present invention published a result of observation on the shape and the distribution of pores existing in an amorphous material applying a stereoscopic observation method by the transmission electron microscopy (Proceedings of the 49th Joint Meeting on Applied Physics, spring 2002, No. 2, p853 29p-F-3).